Sunday, March 15, 2009

Had a bad day? Erase your memories!

The reputable scientific journal Science just published an interesting article about memories called “Selective Erasure of a Fear Memory”. I especially like the fact that I understand 100% of the words in the title (unlike another article from the same issue, “Generation of Follicular B Helper T Cells from Foxp3+ T Cells in Gut Peyer's Patches”, where I score a meagre 46%).

How memories are stored in the brain has always been a mystery. It is thought that each memory is stored in the form of a group of brain cells (neurons), but it’s practically impossible to confirm that because those neurons are all over the place. We do know, however, that a brain region called the lateral amygdala (LA) is where fear memories are stored. Say you’re just a kid and your older sibling decides to make you watch Poltergeist (am I the only one who went through this?). During the really scary parts of the movie, your neurons in the LA make a ton of this protein called CREB (yet another acronym, it stands for cyclic adenosine monophosphate response element binding protein). That’s the tell-tale sign the researchers used to try to identify and then destroy the neurons responsible for fear memories.

They used an experiment called fear training (sounds like torture? Just think about all the people who willingly volunteered to be on “Fear Factor”). They put a mouse in a special cage, and then they play a tone. Right after the tone, the mouse gets a little shock on its feet. The mouse eventually catches on, and freezes when the tone is played (freezing behavior is how we know the mouse is scared). The really clever part of this experiment is that the researchers managed to engineer in the mouse a genetic switch that would selectively kill the neurons that made a lot of CREB (the ones presumably responsible for the fear memory). So after training the mouse to be scared of the tone, they flipped the switched on, the CREB-making neurons died, and voilà! The mouse forgot its fear of the tone and no longer freezes.

So, ok, researchers fried part of this mouse’s brain, and the mouse won’t freeze anymore. Sure, but will the mouse do anything anymore? I don’t know about you, but I’m picturing the mouse in a post-lobotomy state, drooling a little, unmotivated to do anything. Apparently not so. The researchers did a bunch of control experiments to show that the mouse could still run through mazes, store new memories, and even re-learn to be afraid of the tone, if properly trained. They also showed that if you just kill a bunch of random LA neurons (instead of just the ones that make lots of CREB), erasing memories doesn’t work.

So is this relevant? Well, it’s a great contribution to our knowledge of how memories are encoded and stored. A lot of people are excited about this because they see a potential therapy for post-traumatic stress disorder, but to be fair, applications in humans are very, very far down the road, regardless of what the movie “Eternal Sunshine of the Spotless Mind” suggests. If you had a choice, would you erase some bad memories of your past? How did those memories shape the person you are today?

3 Responses to “Had a bad day? Erase your memories!”

Autumn said...

Ack! You're taking me back to my undergrad Cognitive Psych class with this talk! :) Are we talking about completely erasing the bad memories, like those events never happened? If so, behavioral psych suggests we would lose knowledge and do things we learned not to do, i.e. completely stumbling when asking someone one (which I still do often!). Plus, I believe the total sum of my experiences, good and bad, make me who I am today: the strong, vibrant, resilient woman I've become.

But, would I like to reduce the power of some of those bad memories? Sure, I'd go for that. If I could take some of the lasting "sting" away and take away the rumination of bad memories, I'd be all for that. But, I think that's going to require more of a cognitive-behavioral therapy approach as opposed to a psychiatric approach.

(BTW: I found your blog through a comment you made on the IBKC, just in case you're wondering.)

Dr. Julie said...

Hey Autumn!
Yup, I think the authors are suggesting the memory is completely gone, like it never happened. Like you suggest, losing some knowledge could be a dangerous thing. I always think of the whole hand-on-the-stove example. Sure, I'd love to erase the memories associated with an ex-boyfriend or two, but I did learn a lot in the process, and I certainly wouldn't want to lose that knowledge. And, like you, I also believe I'm the sum of my good and bad experiences, and that makes me who I am. But I'm pretty lucky in that I haven't gone through anything especially traumatic, so I might feel differently if I had.

Thanks for your comment! I love IBKC...

It would be interesting to know how this played in repressed memories and why one person would remember a traumatic event in great detail, but another person (for instance, a sibling) would completely repress it.

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